I was one of the first people to arrive at Riverbanks Zoo early on the morning of Oct. 4, 2015, the day of the “Great Columbia Flood.” The Lower Saluda River had overflowed its banks, and floodwaters covered Riverbanks’ perimeter road for the first time in zoo history. I jumped into a golf cart and made my way around the back of the zoo where a 10-foot-high chain-link fence separated the zoo from the surrounding forest and river, usually a 200-foot-wide swath of thick underbrush and massive hardwood trees.
On this day, the river covered the forest and road in more than two feet of rapidly flowing, muddy water. I drove slowly down the road, water rushing over the cart’s floorboard, when I noticed a dog trapped against the outside of the fence, desperately swimming against the still-rising water. As I approached the frantically swimming “dog,” I realized it was not a dog at all, but an adult beaver. Continuing on I would discover two more beavers swimming along the fence. Yes, beavers live inside Columbia’s city limits.
The beaver (Castor fiber) is North America’s largest rodent, which is the biggest classification of mammals, characterized by upper and lower pairs of ever-growing rootless incisor teeth. It can be found throughout the continent, from Alaska and Canada into northern Mexico. The head-body-tail length of adult beavers can range from 37 to 50 inches. Beavers are stocky; older males may weigh more than 80 pounds with a record of an astounding 100 pounds. Females are smaller, averaging around 30 pounds. Beavers are vegetarians. Like their South American counterparts, the capybara, they are semi-aquatic and have several adaptations for life in the water: their hind feet are webbed; nostrils and ears are closable; and transparent membranes cover their eyes when swimming underwater.
Their most prominent feature is a broad, flat tail. It serves a variety of purposes, from acting as a prop for sitting upright (beavers actually sit on their tails, which are tucked under their bodies) and a rudder when swimming. The hairless tail is also used to warn others of danger by slapping the surface of the water. Fat may be stored in their tail to aid in winter survival.
Their scientific name is derived from a pair of scent glands, called castors, at the base of their tails. Secretions from these glands are used to mark territory. Beavers have large teeth, which continue to grow throughout their lifetime. Their upper incisors are about an inch long. These same incisors are typically orange or brown due to the presence of iron in the tooth enamel, an adaptation to assist in cutting through hard wood.
One of the most recognizable behaviors of beavers is the construction of dams and lodges. Dams are constructed out of trees and branches that are cut using their strong front teeth. Dams are typically built across small streams to create a pond. In early autumn, a den or “lodge” is built in the pond in order to raise young and provide protection from predators. Interestingly, the lodge is abandoned in springtime and may never be used again. Beaver ponds are viewed by people with mixed emotions. On the one hand they create new wetlands, thus providing home for a variety of wildlife, while on the other dams can result in significant flooding and property damage.
By the end of the 19th century, beavers were actually eradicated in South Carolina due to uncontrolled trapping. They were reintroduced in the eastern portion of the state in 1940. The population began to expand, and beavers can now be found in all 46 South Carolina counties. Some portions of the state consider them a problem, and trappers are utilized to remove nuisance beavers.
Like most cities around the world, Columbia is experiencing a boom in urban wildlife. Alligators can be found in streams and canals around the city, and white-tailed deer roam our backyards, destroying shrubs and flowers. We can now add beavers to that list. Whether this invasion is good or bad is truly in the eye of the beholder. And what about those three beavers trapped against the zoo’s fence? Our staff continued to observe them over the course of the morning until they swam out into the still rising river.